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Milner Hall yields first hominin fossils

Sterkfontein is a set of limestone caves near Krugersdorp, South Africa. It is one of the most important hominin fossil-bearing sites in the world and finds include the female australopithecine Mrs Ples, discovered in 1947 and recently voted No.95 in a list of 100 Great South Africans. Sterkfontein has yielded stone tools in addition to hominin fossils and it is now part of the Cradle of Humankind, a World Heritage Site named by UNESCO in 1999. Most of the finds have been made in Members 4 and 5 of the cave’s sedimentary sequence, but rather less well known is the large underground chamber known as Milner Hall.

It is from Milner Hall that the discovery is reported of a hominin adult upper right molar (M1) tooth and a proximal phalanx finger bone, probably from a left hand. The chamber has previously yielded only stone tools, and association with these suggests that the fossils are 2.18 million years old.

The tooth is broadly closer to Homo than to Australopithecus or Paranthropus. It most closely resembles the Olduvai OH 6 first molar assigned to Homo habilis and a first molar assigned to the recently-proposed Homo naledi. The shape and size of the tooth’s cusps align it to early Homo.

The finger bone is larger and more robust than that of any hominin so far discovered in South Africa. It resembles the Olduvai Homo habilis fossil OH 7, but is much larger. It is markedly curved, within the range of Australopithecus afarensis and suggesting adaptation for tree-climbing, but it lacks other features associated with arborealism, such as a strongly developed flexor apparatus and a mediolaterally expanded diaphysis; these features are present in A. afarensis, Homo habilis and present-day chimpanzees. The finger bone possesses an enigmatic mixture of primitive, derived and unique characteristics. It is not clear whether or not it belonged to the same individual and its taxonomic affinities are at this stage uncertain.